Method for producing anhydrous sodium dithionite

ABSTRACT

A process for producing anhydrous sodium dithionite, which comprises introducing 10 to 75 % by weight of the amount required for the completion of the reaction, of sulfur dioxide into a mixture of sodium formate and an alkali metal compound at a temperature of 70* to 150*C, and then introducing the remaining 90 to 25 % by weight of sulfur dioxide into the mixture at a temperature of 60* to 85*C.

'United States Patent 1191 Yasue et a1.

[ Nov. 4, 1975 METHOD FOR PRODUCING ANHYDROUS SODIUM DITHIONITE [75] Inventors: Masayuki Yasue, Nara; Sizuo Saito,

Toyonaka; Sumio Shimojo, Suita; Kazuhisa Shiode, Osaka, all of Japan [73] Assignee: Sumitomo Chemical Company, Ltd.,

Osaka, Japan [22] Filed: Oct. 26, 1970 21 Appl. No.: 84,187

[30] Foreign Application Priority Data Oct. 30, 1969 Japan 44-87458 Feb. 5, 1970 Japan 45-10528 [52] US. Cl. 423/515 [51] Int. Cl. C01B 17/66 [58] Field of Search 23/116; 252/188; 423/515 [56] References Cited UNITED STATES PATENTS 3,411,875 11/1968 Yoshikawa et a1. 23/116 3,576,598 4/1971 Plentovich et a1. 23/116 FOREIGN PATENTS 0R APPLICATIONS 1,148,248 4/1969 United Kingdom 23/116 Primary Examiner-Earl C. Thomas Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [57] I ABSTRACT 5* Claims, No Drawings 1 METHOD FOR PRODUCING ANHYDROUS SODIUM DITHIONITE This invention relates to a process for producing aning to the formic acid process, sodium dithionite is formed through the following reactions:

NaOH so NdHso, 1 HCOONa so 1-1,o Hcoo1i Mel-1S0 2 HCOOH 2NaHSO Na S O co2 21-1 3 nydrous sodium dithionite, and more perticularly to an 5 Thus, sodium hydrogensulfite is formed according t; improved method for producing the same from sodium the reactions and and is allowed to react Wit forrnate, sulfur dioxide and an alkali metal compound. formic acid formed simultaneously in the reaction 12) Sodium dithionite is widely used in the field of dyeing Yield sodmmfilthiomte accmdmg and bleaching of fibrous materials owing to its reducing l0 In the formlc acid f the reactlon (3) g ability not proceed unless the reaction temperature excee s 50 C. For example, 1n US. Pat. No. 2,010,615, sulfur There 15 known for example m Pat dioxide is introduced into an alcoholic aqueous solu and h a profess Producmg Sodlum tion of sodium formate and an alkali metal compound dfthlomte compflsmg leactmg'sodlum formzjue sulfur at a temperature of 30C or lower and thereafter the dioxlde and an alkalrmetal compound (hereinafter re- 15 reaction System is carefully heated at or higher, ferred to as the formlc acid Process) and for example, in the examples of British Pat. No. The product obtained according to these known pro- 11,010 and U.S.S.R. Pat. No. 52,052 sulfur dioxide or cesses is in the form of fine powder which renders the an alcoholic solution thereof is introduced into the repractical use seriously troublesome owingto its dusty action system at a temperature of 70C. property. Sodium dithionite is very labile, especially when it is An object of the present invention is to provide a proheated and is p an Pcidic y and 1t cess f producing di di hi i h i i d was considered that the introduction of sulfur d1ox1de, i l i and heating for completion of the reaction must be Other object of the present invention is to provide a consumed under a collidmon whege i dlthaonite process for producing sodium dithionite without acpro ucied must not eFompose T ere t e mcompanying substantial decomposition thereof despite troductlon of Sulfur ihoxlde has boeen conducted at a the reaction is effected at a relatively high temperature, temperanire of not hlgher h 9 Accordmg to the present mventlon, 1n the first stage, Efforts have been dlrected to a study to achieve the 10 to 75% preferably 15 to 40% by Weight of the above F w fi q that the P k 3O amount required for the completion of the reaction, of P Sodium dlthfomte h Y f lmpr9ved pamcle. Slze sulfur dioxide in the form of an alcohol solution is in- 1s feas1ble by effecting the initial reaction at a relatively troduced into a mixture of Sodium formate and an hlgh p kali metal compound at a temperature of 70 to 150C, In connection w1th the above fact, it has also been preferably 72 to 110 d th ft the remaining found that the decomposition of sodium dithionite 35 90 to 25% b i h f lf di id i h f of an formed can be avoided y controlling the reaction alcohol solution is introduced thereinto at a temperaperature during the addition of sulfur dioxide to be ret f to 85C, preferably to 85C, at which the acted. mixture is successively stirred in order to complete the Thus, the present invention provides a process for reaction. Thus, a product having an improved particle producing anhydrous sodium dithionite having im- 40 size may be obtained in a high yield and a high purity. proved particle size in a high yield, which comprises in- The relationship between the reaction temperature troducing part of sulfur dioxide required for the comand the distribution of particle size of the product, sopletion of the reaction to a mixture of sodium formate dium dithionite, is' shown in Table 1.

Table 1 Temperature Introduction Introduction for the of SO -methanol of SO -methanol completion Yield First stage Second stage of the based on Amount Temperature Amount Temperature reaction S02 Purity Particle size (;1)

( d (C) (70 (C) (C) (7:) (71) 105 l05-74 74-46 46 0-100 30 75 s 1 89 0% 0% 0% 100% 0- 100 70 75 82 89 2 17 54 27 0- 50 7s 50- |00 75 75 82 90 3 47 35 14 0- 50 50- 100 75 75 82 89 19 47 2s 7 0- 30 s5 90 30-100 75 75 83 90 30 41 20 s 0-25 25- 100 75 75 s2 s9 42 3s 12 9 "0+1 00 95 100 75 0 decomposed When the total amount required for the completion of the reaction. of SO -methanol was introduced at once at a high temperature. the product was not obtained because of its decomposition.

and an alkali metal compound at a temperature of 70 to C, and then introducing the remaining sulfur dioxide thereto at a temperature of 60 to 85C. Accord- From the following Table 2, it is clear that the particle size of the product depends on the temperature of the first stage.

Table 2 Temperature Introduction Introduction for the of SU -methanol of SO -methanol completion First stage Second stage of the Amount Temperature Amount Temperature reaction Particle size (M) (l- 75 80 75 l00 70 7O 2O O 8 75 80 75- l00 80 80 27, 26 38 7 0- 25 95 100 l00 75 75 42 35 12 9 O-FZS 95 I00 25- l0() 80 8O 84 39 38 I4 8 The present invention will be explained in more detail as follows.

The alkali metal compound used in the present process is sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium hydrogensulfite, sodium metabisulfit'e,' sodium sulfite or a mixture thereof and it is preferable to use sodium hydroxide. In case where at least one of said sulfites is used as the alkalimetal compound, it is needless to say that an amount of sulfurdioxide may be deducted. The alcohols used in the pres. ent invention are methanol, ethanol and a mixture thereof. It is preferable from economical point of view to use methanol. In carrying out the present process, the use of an alcohol solution of sulfur dioxide is more preferable than the use of gaseous sulfur dioxide. The U.S.S.R. Pat. No. 52,052 also discloses the advantages due to the useof an alcohol solution of sulfur dioxide that the use of the solution is easy to handle and results in preventing the decomposition of sodium dithionite produced, because the reaction mixture may be prevented from a partial strong acidification, as the acidification is moderated by the formation of a complex between sulfur dioxide and an alcohol and by the addition of the complex formed in a dilute state. A concentration of sulfur dioxide in the alcohol is 20 to 35 by weight, preferably 22 to by weight.

A mixture of sodium formate and the alkali metal compound is dissolved or suspended in water or a mixture of water and an alcohol. It is needless to say that the alcohol recovered by means of distillation after the completion of the reaction, may be used as a source of an alcohol. The alcohol recovered may contain a small amount of a formic acid ester. When the reaction of the first stage in the present process is conducted at a temperature higher than the boiling point of the solvent used, the reaction is conducted under an increased pressure, for example, by means of the introduction of an inactive gas such as nitrogen or carbon dioxide gas. On the other hand, a suitable pressure may be obtained by the control of carbon dioxide which is produced as the reaction proceeds to produce sodium dithionite.

In carrying out the present process, the preferable amount ratio of the materials will given as follows. When sodium hydroxide and methanol are used respectively as the alkali metal compound and the alcohol, on the basis of 64 parts of sulfur dioxide, 42 to 80 parts of sodium formate, 12 to 22 parts of sodium hydroxide, 42 to 80 parts of water and 190 to 300 parts of methanol are used, all the parts being by weight. In the case where the alcohol containing a formic acid ester is used, sodium hydroxide may be used in an amount larger than that described above, because part or all of the formic acid ester contained in the alcohol is conthe process of the invention has such advantages as 1 good flowability and stability due to its monocrystal.

The invention will be explained in more detail by referring to the following Examples, which are, of course, not to limit the scope of the invention. Parts and percent mentioned each are by weight.

EXAMPLE I 120 Parts of sodium formate, 90 parts of water, 67 parts of a 48 percent aqueous solution of sodium hydroxide and 100 parts of methylalcohol were mixed in an autoclave under a pressure of -1 Kg/cm (Gauge) with nitrogen at a temperature of C.

While maintaining the temperature at 75 to C, a solution containing 128 parts of sulfur dioxide in 380 parts of methyl alcohol was added thereto over a period of 3 hours and the mixture was kept at the same temperature for additional 3 hours.

During the reaction, carbon dioxide generated was gradually removed to maintain the pressure at l Kg/cm (Gauge), and the temperature was kept at 75 to 80C. After the reaction was over, the content of the autoclave was allowed to cool to 50C, and filtered under nitrogen atmosphere. The solid separated was washed sufficiently with methyl alcohol, dried under reduced pressure or under nitrogen atmosphere. Thus, 143 parts of anhydrous sodium dithionite was obtained in a purity of percent. The product was not dusty and its particle size distribution is shown in the following Table 3.

A mixture of 120 parts of sodium formate, 90 parts of water, 67 parts of a 48 percent aqueous solution of sodium hydroxide and parts of methyl alcohol was heated to 80C under a pressure of 1.0 Kg/cm (Gauge) with nitrogen. To the mixture, a solution containing 64 parts (50 of the amount required for the completion of the reaction) of sulfur dioxide in 190 parts of methyl alcohol was added at 80C, and thereafter the temperature was lowered to 73C. At said temperature, a solution containing 64 parts (50 of the amount required for the completion of the reaction) of sulfur dioxide in 190 parts of methyl alcohol was added to the mixture during 3 hours. The mixture was further kept at 73 80C for additional 3 hours, during which carbon dioxide produced was gradually removed out of the reaction system to keep the pressure at 1.0 Kg/cm (Gauge). After the reaction was over, the subsequent procedures were carried out as described in Example 1. 143 Parts of anhydrous sodium dithionite having a purity of 90 percent was obtained. The particle size distribution of the product is shown in the following Table 4.

Table 4 Particle size (it) 105 105-74 74-46 46 Distribution EXAMPLE 3 A mixture of 120 parts of sodium formate, 90 parts of water, 67 parts of a 48 percent aqueous solution of sodium hydroxide and 100 parts of methyl alcohol was heated to 95C under a pressure of 1.5 Kg/cm (Gauge) with nitrogen. To the mixture, a solution containing 32 parts (25 of the amount required for the completion of the reaction) of sulfur dioxide in 95 parts of methyl alcohol was added at 95 to 100C, and thereafter the temperature was lowered to 75C. At said temperature, a solution containing 96 parts (75 of the amount required for the completion of the reaction) of sulfur dioxide in 285 parts of methyl alcohol was added to the mixture during 3 hours. The mixture was further kept at 75C for additional 3 hours, during which carbon'dioxide produced was gradually removed out of the reaction system to keep the pressure at 1.5 Kg/cm (Gauge). After the reaction was over, the temperature was lowered to a temperature of 50C or less and the reaction mixture was filtered under nitrogen atmosphere to separate crystals, which were washed sufficiently with methyl alcohol and dried under a reduced pressure or nitrogen atmosphere. Thus, 142 parts of anhydrous sodium dithionite having a purity of 89 was obtained. The particle size distribution is shown in the following Table 5.

Table 5 Particle size (n) 105 [05-74 74-46 46 Distribution EXAMPLE 4 6 The subsequent procedures were same as described in Example land 144 parts of anhydrous sodium dithionite having a purity of percent was obtained.

The particle size distribution of the product is shown in the following Table 6.

A mixture of parts of sodium formate, partsof water, 50 parts of sodium sulfite and 170 parts of methyl alcohol was once heated to 9095C under a pressure of 2 Kg/cm (Gauge) of nitrogen in an autoclave. Then, the content of the autoclave was allowed to cool to 80C, and added with 400 parts of a methanol solution containing 100 parts of sulfur dioxide over a period of 2.5 hours. The subsequent procedure was carried out as described in Example 1, and 142 parts of sodium dithionite having a purity of 89 percentwas obtained.

The particle size distribution of the product is shown in Table 7.

What is claimed is:

1. In the preparation of anhydrous sodium dithionite by a process wherein sulfur dioxide is mixed with sodium formate and an alkali metal compound, the method which produces anhydrous sodium dithionite of improved particle size which comprises adding a methanol solution of sulfur dioxide to a solution or suspension of sodium formate and an alkali metal com pound in two steps with from about 10 to about 75 by weight of the total sulfur dioxide used being mixed with the solution or suspension of sodium formate and alkali metal compound at a temperature of 70C. to C. in the first step and the remainder of the sulfur dioxide being added in a second step at a lower temperature within the range of 60C. to 85C.

2. A process according to claim 1, wherein a concentration of sulfur dioxide in the alcohol is 20 to 35 by weight.

3. A process according to claim 1, wherein the mixture of sodium formate and the alkali metal compound is dissolved or suspended in water or a mixture of water and an alcohol.

4. A process according to claim 1, wherein the alkali metal compound is sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium hydrogensulfite, sodium metabisulfite, sodium sulfite or a mixture thereof.

5. A method for making sodium dithionite of improved particle size which comprises preparing an aqueous solution or suspension of sodium formate and an alkali metal compound and adding to the resulting aqueous solution or suspension a methanol solution of sulphur dioxide in two steps with from about 10 to about 75 by weight of the sulphur dioxide being added 75 the solution or suspension at a temperature of Q o 70C. to 150C. ina first step and the remainder of the temperature wlthm the range of 60 to 85 sulphur dioxide being added in a second step at a lower 

1. IN THE PREPRATION OF ANHYDRODROUS DITHIONITE BY A PROCESS WHEREIN SULFER DIOXIDE IS MIXED WITH SODIUM FORMATE AND AN ALKALI METAL COMPOUND, THE METHOD WHICH PRODUCES ANHYDROUS SODIUM DITHIONITE OF IMPROVED PARTICLE SIZE WHICH COMPRISES ADDING A METHOD SOLUTION OF SULFUR DIOXIDE TO A SOLUTION OR SUSPENSION OF SODIUM FORMATE AND A ALKALI METAL COMPOUND IN TWO STEPS WITH FROM ABOUT 10% TO ABOUT 75% BY WEIGHT OF THE TOTAL SULFER DIOXIDE USED BEING MIXED WITH THE SOLUTION OR SUSPENSION OF SODIUM FORMATE AND ALKALI METAL COMPOUND AT A TEMPERATURE OF 70*C TO 150*C. IN THE FIRST STEP AND THE REMAINDER OR THE SULFER DIOXIDE BEING ADDED IN A SECOND STEP AT A LOWER TEMPERATURE WITHIN THE RANGE OF 60*C TO 85*C.
 2. A process according to claim 1, wherein a concentration of sulfur dioxide in the alcohol is 20 to 35 % by weight.
 3. A process according to claim 1, wherein the mixture of sodium formate and the alkali metal compound is dissolved or suspended in water or a mixture of water and an alcohol.
 4. A process according to claim 1, wherein the alkali metal compound is sodium hydroxide, sodium carbonate, sodIum bicarbonate, sodium hydrogensulfite, sodium metabisulfite, sodium sulfite or a mixture thereof.
 5. A method for making sodium dithionite of improved particle size which comprises preparing an aqueous solution or suspension of sodium formate and an alkali metal compound and adding to the resulting aqueous solution or suspension a methanol solution of sulphur dioxide in two steps with from about 10 % to about 75 % by weight of the sulphur dioxide being added 75 the solution or suspension at a temperature of 70*C. to 150*C. in a first step and the remainder of the sulphur dioxide being added in a second step at a lower temperature within the range of 60*C. to 85*C. 